Background

Germany was stripped of its U-boats by the Treaty of Versailles at the end of World War I, but in the late 1920s and early 1930s began to rebuild its armed forces. The pace of rearmament accelerated under Adolf Hitler, and the first Type II U-boat was laid down on 11 February 1935. Knowing that the world would see this step towards rearmament, Hitler reached an agreement with Britain to build a navy up to 35% of the size of the Royal Navy in surface vessels, but equal to the British in number of submarines. This agreement was signed on 18 June 1935, and U-1 was commissioned 11 days later.

Design

The defining characteristic of the Type II was its small size. Known as the Einbaum ("dugout canoe"), it had some advantages over larger boats, chiefly its ability to work in shallow water, dive quickly, and increased stealth due to the low conning tower. However, it had a shallower maximum depth, short range, cramped living conditions, and couldn't carry as many torpedoes.

The boat had a single hull, with no watertight compartments. There were three torpedo tubes forward (none aft), with space for another two torpedoes inside the pressure hull for reloads. A single 20 mm anti-aircraft gun was provided, but no deck gun was mounted.

Space inside was limited. The two spare torpedoes extended from just behind the torpedo tubes to just in front of the control room, and most of the 24-man crew lived in this forward area around the torpedoes, sharing 12 bunks. Four bunks were also provided aft of the engines for the engine room crew. Cooking and sanitary facilities were basic, and in this environment long patrols were very arduous.

Most Type IIs only saw operational service during the early years of the war, thereafter remaining in training bases. Six were stripped down to their hulls, transported by river and truck to Linz (on the Danube), and reassembled for use in the Black Sea against the Soviet Union.

In contrast to other German submarine types, few Type IIs were lost. This reflects their use as training boats, although accidents accounted for several vessels.

These boats were a first step towards re-armament, intended to provide Germany with experience in submarine construction and operation and lay the foundation for larger boats to build upon. Only one of these submarines survive; the prototype CV-707, renamed Vesikko by the Finnish Navy which later bought it.

On 3 February 2008, The Telegraph reported that a U-20 had been discovered by Selçuk Kolay (a Turkish marine engineer) in 80 feet (24 m) of water off the coast of the Turkish city of Zonguldak. According to the report, Kolay knows where U-23 and U-19 submarines are, scuttled in deeper water near the U-20.[2]

Comparison of Finnish Crichton-Vulcan CV-707(U2A) to German Type II

CV-707

Type IIA U1-U6

Launched

11 May 1933

1939–1940

Displacement (tonnes)

Surfaced

254

254

Submerged

303

303

Total

381

381

Size (metres)

Length

40.90

40.90

Beam

4.10

4.10

Draft

4.20

3.80

Speed (knots)

Surfaced

13

13

Submerged

8

6.9

Range (nautical miles)

Surfaced

1,350 nmi (2,500 km; 1,550 mi) at 8 knots (15 km/h; 9.2 mph)

1,000 nmi (1,900 km; 1,200 mi) at 8 knots (15 km/h; 9.2 mph)

Submerged

40 nmi (74 km; 46 mi) at 4 knots (7.4 km/h; 4.6 mph)

35 nmi (65 km; 40 mi) at 4 knots (7.4 km/h; 4.6 mph)

Engine

Diesel-electric

Diesel-electric

2 × MWM Diesel 700 PS (690 shp; 510 kW)

2 × MWM Diesel 700 PS (690 shp; 510 kW)

2 × SSW Electric 360 PS (360 shp; 260 kW)

2 × SSW Electric 402 PS (397 shp; 296 kW)

Type IIA

The Type IIA was a single hull, all welded boat with internal ballast tanks. Compared to the other variants, it had a smaller bridge and could carry the German G7a, G7e torpedoes as well as TM-type torpedo mines. There were two periscopes in the conning tower; an aerial (navigation) periscope at the front of the tower, and an attack periscope in the middle of the tower. There were serrated net cutters in the bow. The net cutters were adopted from World War 1 boats but were quickly discontinued during World War 2.

List of Type IIA submarines

Type IIB

The Type IIB was a lengthened version of the Type IIA. Three additional compartments were inserted amidships which were fitted with additional diesel tanks beneath the control room. The range was increased to 1,800 nautical miles at 12 knots. Diving time was also improved to 30 seconds.

List of Type IIB submarines

Type IIC

The Type IIC was a further lengthened version of the Type IIB with an additional two compartments inserted amidships to accommodate improved radio room facilities. The additional diesel tanks beneath the control room were further enlarged, extending the range to 1,900 nautical miles at 12 knots.

List of Type IIC submarines

Type IID

The Type IID had additional saddle tanks fitted to the sides of the external hull. These saddle tanks were used to accommodate additional diesel storage tanks. The diesel oil would float atop the saddle tanks. As oil was consumed, water would gradually fill the tanks to compensate for the positive buoyancy. The range was nearly doubled to 3,450 nmi (6,390 km; 3,970 mi) at 12 knots (22 km/h; 14 mph) and enabled the Type II to conduct longer operations around the British Isles. A further development was the propellers were fitted with Kort nozzles, intended to improve propulsion efficiency.